Traditionally a seat belt safety restraint comprises a length of belt webbing connected at three points to load bearing parts of a vehicle. Typically one end is bolted to a door sill on one side of the seat, arranged to pass laterally across the hips of the vehicle occupant to a buckle mechanism fixed to the vehicle on the opposite side of the seat, and then diagonally across the torso of the vehicle occupant to a further fastening point on the B pillar of the door. The buckle mechanism engages a buckle tongue attached to the belt webbing in a slidable manner.
To increase comfort for the vehicle occupant restrained by the belt, a retractor is fitted at the pillar end of the webbing. This allows the webbing to pay out under relatively low loads to enable limited movement of the restrained vehicle occupant, for example to reach in-car entertainment controls or storage compartments. The retractor is biased to keep the webbing relatively taut about the vehicle occupant and a locking element is included to lock the retractor against webbing pay out in the event of a dangerous situation being detected. For example, an acceleration sensor activates if the vehicle undergoes rapid acceleration or deceleration indicative of a crash.
In recent years, pretensioners have been introduced to rapidly pull in a length of webbing to actively tighten the belt about the vehicle occupant in the event of a crash condition being sensed. This takes up any slack that may have
developed in the belt and helps to more correctly position the vehicle occupant in the seat to maximise the effect of the belt protection and of any secondary safety restraint such as an airbag.
Pretensioners comprise a force reservoir such as a pyrotechnically operated gas generator to provide an impulse of sufficient magnitude to tighten the belt in a short space of time, ideally before the crash pulse takes full effect. A typical known pretensioner uses rotational means to wind in a length of seat belt webbing, for example by rotating the retractor spool in a webbing rewind direction to take in the required length of webbing prior to the retractor locking against webbing pay out.
However, known pretensioners tend to be bulky, and are particularly difficult to use for the driver, and front passenger, seat of a three door vehicle because of the requirement to allow access to the rear of the vehicle past the front seats. Using a traditional retractor pretensioner mechanism in a front seat of a three door vehicle causes an unacceptable obstruction.
Seat travel is greater in a three door vehicle than in a four door vehicle in order to provide such access and to accommodate this the door sill end of the webbing is usually attached to a so-called slider bar of well known design, instead of being fixedly bolted to the floor. This allows the sill end of the webbing to be moved longitudinally forward and rearward to facilitate rear seat access and front seat movement.
The present invention provides an improved pretensioning mechanism that can be used in three-door, front seat applications.